You know, I've never had mould grow in any of my CamelBak bladders, and I can be pretty slack about cleaning them (although I do only ever have water in 'em). One of them had a bitevalve that kinda tasted of dirt, but when I looked at it I saw, well, dirt so I stopped worrying about the taste.

I remember trying to get some mould out of a bottle once years ago. Detergent, hot water and a brush didn't work, so I bleached the living daylights out of the little sucker. You don't need as much bleach as you might think - had to toss that drink bottle because I couldn't get the chlorine taste out of it!